Hydrocarbon prospecting



y 1962 L. R. BROWN 3,033,761

HYDROCARBON PROSPECTING Filed Sept. 3, 1959 APPROXIMATE LIMITs OF OIL I=IELD 11;

\ v A u 40 .0 l

0 I 0 t 8' l 0 l 5" V a" n APPROXIMATE LIMITS I OF OIL FIELD R o- 4 0- a L 0 O- 2 1. O- l oo E .0

. NUMBER OF HYDROCARBON sPEcIEs usED (I) 5 t3 APPROXIMATE LIMITS 4 0. OF OIL FIELD 3 In I 6 O E a IIIIIIIIIIIIIIIIIIII A LOCATION OF SAMPLES B I II) APPROXIMATE LIMITS 9 OF oIL FIELD c 3 O 2 an MD 0-I S g INVENTOR. IIIIIIIIIIIIIIIIIII A LocATIoN OF SAMPLES B I BY DALE NM AGENT United States Patent Ofiice 3,Q33,76l Patented May 8, 1362 3,033,761 HYDROCGN PRUSPEt'ITING Lewis R. Brown, Baton Rouge, La. (Rte. 1, Box 204, Starkville, Miss.) Filed Sept. 3, 1959, Ser. No. 837,860 8 Claims. (Cl. 195-1035) This invention relates to methods of prospecting for oil and gas, and more particularly to an improved microbiological prospecting method involving earth or soil sampling.

Subterranean accumulations of hydrocarbon such as oil and gas nearly always occur in sedimentary strata, and generally accumulate in a particular place because of the presence of a relatively impervious stratum or other stratigraphic discontinuity. However, such sedimentary strata are impervious only from a relative standpoint, and it is well known that seepage may occur during geological periods of time from deposits of oil and gas even when the cap rock or other stratigraphic discontinuity bounding the petroleum deposits has a very low permeability.

It is to be expected, accordingly, that indications may be obtained as a general rule at or near the surface, of petroleum deposits situated at a considerable depth. While gross indications such as seepages have been used in petroleum prospecting since the beginnings of the industry, it has been realized for upwards of twenty-five years that the systematic determination of minute traces of hydrocarbons in surface samplings would give a pattern from which the presence of underlying petroleum deposits might be discerned. The practical application of this general principle, however, has been largely disappointing. One obvious diificulty arises from the anisotropy of sedimentary formations generally, particularly when an area comprising several miles in extent is considered. The various strata not only have different diffusion rates for the several hydrocarbons involved, different both as to stratum and as to hydrocarbon, but various strata and surface soils and the like have widely different abilities to retain traces of hydrocarbons so as to'provide a basis for sampling. The extreme heterogeneity of the strata, of the soils, the hydrocarbons, and the like which are involved have made it not at all clear what sampling method, or set of testing methods, might lead to productive results. For example, soils and even deeper lying near-surface strata have been sampled and later subjected to chemical analysis for hydrocarbons, while other workers have sampled the soil air and determined hydrocarbons in the latter. Although much exploratory work has been done, known methods of prospecting by chemical analysis either of surface soil or of soil air have not been perfected to the point where they may be used as a reliable guide for drilling a Well.

A somewhat diiferent approach has been used by other workers in this art, in that the hydrocarbons presumptively present in the soil samples have been tested not by direct chemical analysis, but rather by methods which depend upon the presence of soil bacteria which have the property of consuming hydrocarbons. The general principle upon which such microbiological methods rest is that over a long period of time, where hydrocarbons seep to the surface from underlying petroleum deposits, the proliferation of hydrocarbon-consuming bacteria will be favored, while in areas remote from petroleum deposits such bacteria will be relatively scarce.

Here again, the possibilities of sampling and testing are considerable, and it is an unfortunate fact that various methods which have heretofore been proposed do not give consistent results, and do not lead to the finding of petroleum deposits, which after all is the acid test of any prospecting method.

For example, apparatus containing culture media has been lowered into test borings, allowed to remain a period of time, and withdrawn and observed. Again, soil samples have been investigated by methods depending upon the production of fluorescent compounds by hydrocarhon-consuming entities. Still further, soil samples have been used to inoculate culture media in the laboratory. Representative of the varied approaches are Taggart Patent 2,349,472, Hassler Patent 2,321,293, Strawinski Patent 2,665,237, Updegraif Patent 2,861,921, Hitzman Patent 2,880,142, Blau Patent Re. 22,345, and Sanderson Patent 2,294,425.

The fundamental difliculty with microbiological methods of prospecting is that the detection of diffused petroleum gases by means depending upon microorganisms present in the soil is at best a highly indirect one. Unlike a routine chemical analysis for say carbon in steel, one is forced to rely upon determinations which do not determine directly diffused petroleum present in the soil. The extremely small size of the organisms concerned further complicates the problem, as do the variable responses of the organisms to their environment. The very multiplicity of methods which have been proposed is testimony to the difiiculty of the problem.

An object of the present invention is to provide a method for prospecting for petroleum by microbiological methods in such a fashion that the margin of probable error in locating hydrocarbon shows is minimized, particularly as compared to known methods.

Another object of the present invention is to provide a reliable method for prospecting of the type concerned which is relatively simple in execution and adaptable to a Wide variety of soil types and prospecting regions.

Other objects of the invention appear as the description thereof proceeds.

Generally stated, and in accordance with an illustrative embodiment of the invention, I carry out prospecting in accordance with my invention over a given region to be investigated by taking samples of the soil, rocks, sediments, or other earth material at a plurality of locations traversing the given region, and, for any one prospecting survey, generally taken at about the same approximate depth. These samples are taken to a laboratory, which may be at a fixed location or may be a mobile one taken to the general scene of operations, and the samples are subjected to a testing procedure which comprises a series of steps. First of all, the sample representing each location (and a number of samples taken say within a few feet of each other may be composited so as to be more truly representative of the specific location) is divided into several aliquots. Each group of aliquots thus represents a single sampling location. The aliquots are then separately, for each sample location, subjected to a microbiological test to determine the presence of microfiora capable of consuming a single hydrocarbon species chosen from the lower hydrocarbons higher than methane, viz., ethane, propane, isobutane, normal butane and neopentane (2,2-dimethylpropane). For a given group of aliquots, one of each is subjected to such a test for at least three of the hydrocarbon species mentioned. As a result of my experimental findings, I disregard a number of criteria to which various investigators in the past have attached some importance, such as any and all tests with methane, since it is so commonly produced in swamps and other locations having no connection whatsoever with underlying petroleum deposits; the so-called lag time which is the period of time, usually in days,

equired for consumption of the hydrocarbon to begin to an appreciable extent; or the rate at which the hydrocarbons are consumed.

What I have found to be reliably indicative of the presence or absence of microfiora associated with undere or less straight line. plotting is shown in FIGURE 2, which represents such for the test.

lying petroleum deposits is the total number of hydrocarbon species of the type mentioned which are consumed by an earth sample from a specific location. Accordingly, I give the earth samples adequate opportunity for consuming a given hydrocarbon species, and note whether the consumption takes place, or not at all.

I then relate the total number of species of hydrocarbons consumed by the earth sample for a given location -to that location, which is most readily done by making a plot showing the sample locations on a map of the region prospected, and associating the total number of hydrocarbon species consumed for each sample by appropriate graphical means. An example appears in FIGURE 1, which represents an actual survey carried out in accordance with the invention between two known oil fields.

Additionally, or alternatively, it will be found in some cases desirable to construct a traverse of a given region investigated, plotting for example the total number of hydrocarbon species consumed as ordinates against the sample locations as abscissae. This is particularly useful when a number of samples have been taken along a more An example of such a method of a traverse taken along the dotted line shown in FIG- URE 1.

Details of my inventive process may be conveniently disclosed by relating the best method which I know to carry out the invention.

In this best method, which is likewise illustrative of V the invention generally, I stake out a number of locations covering a region to be investigated. The number of locations will be determined by the general topography, the over-all size of the region to be investigated, and the laboratory time available for carrying out the particular survey. Generally speaking, in open country not filled with obvious discontinuities such as hills, g oss faults appearing at the surface, visible anticlines, and the like, the locations will be spaced from /5 to A of a mile apart. While a single sample may be taken from each location, when time permits I prefer to take between three and five separate samples about 20 ft. apart but all within a 50 ft. circle, at a given sample location.

These separate samples are composited for each location by sample mixing, and should total at least a kilogram. As will be set forth hereinhelow, the survey in accordance with the invention may be carried out over a variety of regional types, even including lake bottoms, but the generally best procedure of which I know so far is to sample the soil at a relatively shallow depth, generally between 6 in. and 2 ft. If the soil has recently been plowed, it

is best to sample 6 in. below the lowermost plowed re gion. On the other hand, in some cases soil as such will be absent, merely a weathered zone being exposed, in which case an earth sample at a depth of at least 6 in.

will be taken.

' found that refrigeration at about 40 F. is very desirable,

and permits reliable test to be made even a week or two after the samples have been taken.

The samples are taken to the laboratory, and each sample is thoroughly mixed so that any portion taken therefrom will be representative of the sample location. The sample is divided into a number of aliquots, so as to permit the testing, separately for each aliquot of the re- -spon=e to the individual hydrocarbon species selected While it is possible to divide the soil or earth sample itself, I prefer, and it is the best method which I know, to make a master slurry from the sample, taking a portion of this master slurry and making a second slurry, this slurry then being divided into the desired aliquots, which is facilitated by the semiliquid nature of the slurry. This I accomplished by taking a volume of 1500 cc. of the soil or earth sample, as bulk volume, and making a slurry with 1000 cc. of a suitable aqueous nutrient. For most soil samples taken at shallow or moderate depths it suffices merely to prepare this slurry in a stainless steel container such as a mixing bowl, agitating with a hand drill fitted with a mixing blade. On rare occasions, the soil or earth sample may be so indurated that it will not readily form a slurry by simple hand stirring. In this case, a porcelain ball mill is used in knownfashion to produce a homogeneous slurry. Of this slurry I take 250 cc. and mix it with an additional 500 cc. of the aqueous nutrient and mix in a high speed food mixer such as the Waring Blendor, or a soda fountain mixer. This yields about 750 cc. of slurry which will contain about 25% to 30% solids, depending upon the nature of the soil sample. 50 cc. portions, constituting the aliquots mentioned, are withdrawn and placed in a suitable culture vessel in contact with an atmosphere containing one of the selected hydrocarbon gases, so that if in the aliquot portion of soil slurry there are any bacterial flora which are capable of consuming the particular hydrocarbon species used, this may be noted by some change, such as pressure or volume.

The best apparatus which I have found for carrying out this step is the Stihngen apparatus as modified by Hutton and ZoBell and set forth in detail by them in the Journal of Bacteriology, volume 58, page 464 (1949).

Any suitable nutrient medium may be used. The one which I have found best for ordinary soil samples is a modification of that used by Kaserer, referred to in the Hutton and ZoBell paper cited, consisting of the follow- KNO gms 1.0 MgSO.,- 7H O g ns 0.2 K HPO 3H O gms 0.5 FeCl 6H O gms 0.05

Distilled water to 1 liter.

I find it best to adjust the soil-nutrient mixture to a pH of 7 using sodium hydroxide before commencing the tests. Using 190 cc. prescription bottles for the fiasks, and

placing 50 cc. of the soil-nutrient mixture in the culture bottle, 140 cc. remains in the bottle to be filled by the gas to be tested. Where aerobic bacteria are concerned, as is the case in ordinary soil sampling, the gas mixture which I have found best is the following:

Percent by volume Oxygen 30 Carbon dioxide 5 Hydrocarbon g 65 As explained, the hydrocarbon gas will vary among the several aliquots, and may be, for example, ethane, propane, isobutane and normal butane.

The culture flask assemblies, so prepared, are allowed to incubate at a suitable temperature. I have found F. to be best for ordinary soil samples. Agitation of the incubating vessels or flasks is not necessary during the incubation period, although it is desirable, since the re- .sults are obtained in a somewhat shorter time.

The liquid levels in the vessels are inspected and recorded daily. In general, if an organism is present which consumes the particular hydrocarbon present, a drop in the volume of gas above the culture will be apparent often as promptly as two days, and some cultures will have completed consumption of their hydrocarbon in as short as four or five days. .to fourteen days are average, when consumption takes Generally speaking, seven The distinction between a sample which consumes a particular hydrocarbon and one which does not is readily made, for in the case of a non-consuming sample, the volume change, if any, will be only a few cubic centimeters, rarelyas high as 5 cc.; whereas in the case of a sample which consumes a given hydrocarbon, the volume change for the particular type of cuture flask described will amount to 40 to 55 cc., and substantially never less than about 35 cc. It is thus easy to note the tested samples as positive or negative, that is as go or iino go-9) As a result of extensive tests made on samples from many localities traversing known productive and known non-productive areas, I have discovered that earth strata overlying productive zones give positive results when tested in the manner described on generally all of the hydrocarbon species tested. For example, if four species are tested, over productive horizons the earth samples taken will show three or four species consumed. On the other hand, over non-productive strata, none or perhaps one hydrocarbon species will be consumed. This is clearly evident from FIGURES 1 and 2, which show the result of testing in the manner described for an area joining two known, productive oil fields. In FIG- URE 1, the sample locations are shown, and the figure associated with each sample locality gives the number of hydrocarbon species found to be consumed by the earth sample taken at the location shown. FIGURE 2 shows, in vertical section, the traverse between points A and B on FIGURE 1, taken along the dotted line show thereon.

The lowest and highest values may be smoothed out by lumping together zero and 1, and 3 and4 responses, as is done in FIGURE 3, which corresponds to FIGURE 2 except for this change.

In the illustrative example which has been given, the method shown is particularly adapted to near surface soil samples. However, the invention is equally well operatable for earth strata of a wide variety of types which may overly deeper petroleum bearing horizons. For example, in the case of marshes, it will be necessary to take mud samples from a depth of /2 to 2 or 3 feet below the water-mud contact in the marsh. The same sampling depth is applicable to fresh water lakes, and to tidal inlets and the like.

The invention is equally applicable to oil-shore prospecting, for example in the Gulf of Mexico, in the Channel Island region of Southern California, in the Persian Gulf, and the like. Techniques have been well developed in recent years for sampling the sediment at the sea bottom in such localities, even though the depth from the surface may be hundreds of fathoms, as for example the Emery-Dietz sea-bottom corer (Bull. Geol. Soc. of Am., 52, 16854714 (1941)).

Even in exceptionally arid regions where soil development has taken place scarcely or not at all, the invention is applicable. In such a case, as for example in parts of the Nevada, Arizona and New Mexico desert highlands, earth samples, preferably within the weathered zone, are taken generally at shallow depths, which may be as little as 6 to 12 inches.

While the illustrative example given has been for testing under mesophilic conditions, I do not mean to confine the invention to this temperature range of incubation. For example, where earth samples are taken from generally cold regions, for example from many regions in Alaska, psychrophilic test conditions are preferred, the culture flasks being maintained at temperatures which may be from 40 to 60 F. Psyohrophilic conditions are also indicated for samples of deep-sea sediments, since the environmental temperature for such sediment at considerable depths may be anywhere from 32 F. to about 50 F.

On the other hand, thermophilic conditions are indicated in many cases, as for example certain tidal regions anaerobic conditions.

'cedure and the like.

" of the Gulf and. Florida coasts where the average annual ambient temperature is quite high. In such cases, culture temperatures of to F. will often be found suitable.

Again, While most of the soil samples taken in the average survey over arable or at least non-flooded land more often than not in oil-shore samples, particularly at great depths. In such an event, testing against the various hydrocarbon species is best carried out under A suitable gaseous mixture for such testing consists of the particular hydrocarbon species chosen to the extent of 50 or 60 volume percent with an inert gas such as nitrogen or argon for the remainder.

While the invention has been described with the aid of illustrative specific examples, it will be apparent from the disclosure generally and the nature of my invention that numerous modifications may be made in the apparatus used, the conditions employed, various details of pro- Accordingly, I desire that it be understood that, Within the broad scope of the appended claims, the invention may be practiced otherwise than has been specifically described in the illustrative examples.

Having described my invention, I claim:

1. In a method of prospecting for subterranean deposits of petroleum, the steps comprising: taking earth samples at a plurality of locations within an area to be prospected; taking aliquots of each of said samples, a group of aliquots representing a said sample; and subjecting each of said groups of aliquots to a test to determine the presence of microbiological entities capable of consuming at least three hydrocarbon species chosen from the group consisting of gaseous hydrocarbons higher than methane, each of said chosen hydrocarbons being tested separately on one of said aliquots.

2. In a method of prospecting for subterranean deposits of petroleum, the steps comprising: taking earth samples at a plurality of locations within an area to be prospected; taking aliquots of each of said samples, a group of aliquots representing a said sample; and subjecting each of said groups of aliquots to a test to determine the presence of microbiological entities capable of consuming at least three hydrocarbon species chosen from the group consisting of ethane, propane, isobutane, normal butane, and neopentane, each of said chosen hydrocarbons being tested separately on one of said aliquots.

3. In a method of prospecting for subterranean deposits of petroleum, the steps comprising: taking earth samples at a plurality of locations within an area to be prospected; taking aliquots of each of said samples, a group of aliquots representing a said sample; subjecting each of said groups of aliquots to a test to determine the presence of microbiological entities capable of consuming at least three hydrocarbon species chosen from the group consisting of gaseous hydrocarbons higher than methane, each of said chosen hydrocarbons being tested separately on one of said aliquots; noting the total number of hydrocarbon species consumed by each group of aliquots; and correlating said total number with the location from which said sample was taken.

4. In a method of prospecting for subterranean deposits of petroleum, the steps comprising: taking earth samples at a plurality of locations within an area to be prospected; taking aliquots of each of said samples, a group of aliquots representing a said sample; subjecting each of said groups of aliquots to a test to determine the presence of microbiological entities capable of consuming at least three hydorcarbon species chosen from the group consisting of ethane, propane, isobutane, normal butane, and neopentane, each of said chosen hydrocarbons being tested separately on one of said aliquots; noting the total number of hydrocarbon species consumed by each group of aliquots; and correlating said total number with the location from which said sample was taken.

5. In a method of prospecting for subterranean deposits of petroleum, the steps comprising: taking earth samples at a plurality of locations within an area to be prospected; making each of said samples into a slurry with an aqueous nutrient solution; taking aliquots of each of said slurries, a group of aliquots representing a said sample; maintaining each of said groups of aliquots under incubation conditions under a gaseous atmosphere containing a single hydrocarbon species chosen from the group consisting of gaseous hydrocarbons higher than methane, each of said chosen hydrocarbons being present separately over one of said aliquots, and said chosen hydrocarbons representing at least three hydrocarbon species all of which are higher than methane; and noting the total number of hydrocarbon species not less than three in number and all higher than methane consumed by each group of aliquots.

6. Ina method of prospecting for subterranean deposits of petroleum, the steps comprising: taking earth samples at a plurality of locations withinan area to be prospected; making each of said samples into a slurry with an aqueous nutrient solution; taking aliquots of each of said slurries, a group of aliquots representing a said sample; maintaining each of said groups of aliquots under incu bation conditions under a gaseous atmosphere containing a single hydrocarbon species chosen from the group consisting of ethane, propane, isobutane, normal butane, and

' neopentane, each of said chosen hydrocarbons being present separately over one of said aliquots, and said chosen hydrocarbons representing at least three hydrocarbon species all of which are higher than methane; and noting the total number of hydrocarbon species not less than three in number and all higher than methane consumed by each group of aliquots.

7. In a method of prospecting for subterranean deposits of petroleum, the steps comprising: taking earth samples at a plurality of locations within an area to be prospected; making each of said samples into a slurry with an aqueous ing at least three hydrocarbon species all of which are higher than methane; noting the total number of hydrocarbon species not less than three in number and all higher than methane consumed by each group of aliquots; and correlating said total number with the location for which said sample was taken.

8. In a methodof prospecting for subterranean deposits of petroleum, the steps comprising: taking earth samples at a plurality of locations within an area to be prospected; making each of said samples into a slurry with an aqueous nutrient solution; taking aliquots of each of said slurries, a group of aliquots representing a said sample; maintaining each of said groups of aliquots under incubation conditions under a gaseous atmosphere containing a single hydrocarbon species chosen from the group consisting of ethane, propane, isobutane, normal butane, and neopentane, each of said chosen hydrocarbons being present separately over one of said aliquots, and said chosen hydrocarbons representing at least three hydrocarbon species all of which are higher than methane; noting the total number of hydrocarbon species not less than three in number and all higher than methane consumed by each group of aliquots; and correlating said total number with the location for which said sample was taken.

References Cited in the file of this patent UNITED STATES PATENTS 2,349,472 Taggart May 23, 1944 2,875,135 Maddox Feb. 24, 1959 2,880,142 Hitzman Mar. 31, 1959 

1. IN A METHOD OF PROSPECTING FOR SUBTERRANEAN DEPOSITS OF PETROLEUM, THE STEPS COMPRISING: TAKING EARATH SAMPLES AT A PLURALITY OF LOCATIONS WITHIN AN AREA TO BE PROSPECTED; TAKING ALIQUOTS OF EACT SAID SAMPLES, A GROUP OF ALIPUOTS REPRESENTING A SAID SAMPLE; AND SUBJECTING EACH OF SAID GROUPS OF ALIPQUOTS TO A TEST TO DETERMINE THE PRESENCE OF MICROBIOLOGICAL ENTITIES CAPABLE OF CONSUMING AT LEAST THREE HYDROCARBON SPECIES CHOSEN FROM THE GROUP CONSISTING OF GASEOUS HYDROCARBONS HIGHER THAT METHANE, EACH OF SAID CHOSEN HYDROCARBONS BEING TESTED SEPARATELY ON ONE OF SAID ALIQUOTS. 